MariaDB crash triggered by JSON_TYPE and large MULTIPOLYGON string construction

~~~sql
SELECT x , char_length ( x ) FROM x WHERE x = 't1' ORDER BY x ; SELECT x , x , char_length ( x ) FROM ( SELECT * FROM ( SELECT json_type ( 'true' ) AS x UNION SELECT '2018-11-02 12:34:56.78' UNION SELECT CONCAT ( 'MULTIPOLYGON(((' , REPEAT ( '-0.00000000001234567890123456789012 -0.123456789012345678,' , 1000 ) , '-0.00000000001234567890123456789012 -0.123456789012345678' , 7200 ) UNION SELECT '2018-11-02 12:34:56.78901234' ) AS x ) AS x WHERE x = 't1' ORDER BY x , x ;
~~~

1. 1. Expected result
      The server should either execute the query or return a normal SQL error without crashing.

1. 1. Actual result
      The fuzzing run observed a server crash. The deduplicated stack signature is:
      ~~~
      stack:pthread_kill|raise|abort|timer_settime|__default_morecore|malloc|my_malloc|heap_open_from_share
      ~~~

Top frames:
~~~
pthread_kill
raise
abort
timer_settime
__default_morecore
malloc
my_malloc
heap_open_from_share
~~~